The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft propulsion assembly is made up of a nacelle and a turbojet engine and is designed to be suspended from a fixed structure of the aircraft, for example under a wing or in the fuselage, by means of a suspension mast attached to the turbojet engine or the nacelle.
The turbojet engine typically includes a so-called “upstream” section comprising a fan provided with vanes, and a so-called “downstream” section housing a gas generator.
The vanes of the fan are surrounded by a case making it possible to mount said turbojet engine in the nacelle.
The nacelle has a generally tubular shape comprising an air inlet upstream of the turbojet engine, a middle section designed to surround the fan of the turbojet engine, and a downstream section housing thrust reverser means and designed to surround the gas generator of the turbojet engine. A gas jet nozzle may extend the thrust reverser means in the downstream direction.
The thrust reverser means make it possible to improve the braking capacity of the aircraft by reorienting at least part of the thrust generated by the turbojet engine forward. In the reverse jet position, the thrust reverser means obstruct the gas jet nozzle and orient the discharge flow from the engine toward the front of the nacelle, thereby generating a counter-thrust that is added to the braking of the wheels of the aircraft.
A common thrust reverser means structure comprises a cowl in which an opening is formed designed for the deviated flow, which, in the direct thrust situation of the gases, is closed by the sliding cowl and, in the thrust reversal situation, is released by downstream translation (relative to the direction of flow of the gases) of the sliding cowl, by means of displacement cylinders, said displacement cylinders being mounted on the front frame upstream of the opening.
The sliding cowl is most often made up of two half-cowls, with a substantially semi-cylindrical shape, which are hinged in the upper portion on hinges parallel to the direction of translation of the sliding cowl, and which are closed by bolts in the lower portion.
This arrangement makes it possible, for maintenance operations, to access the inside of the nacelle, and in particular the turbojet engine or an inner structure of the reverser by opening said half-cowls.
In order to resolve certain problems related to a “butterfly” opening, translational opening has also been developed.
In any case, this nacelle structure housing the thrust reverser device undergoes axial aerodynamic forces during flight that tend to cause the structure to withdraw relative to the engine.
So as not to place these forces only on the fastening points of the thrust reverser to a mast, the front frame is connected to the structure of the turbojet engine, and more specifically to the fan case. The connection is traditionally done using a blade/groove system, the male blade portion generally being supported by the front frame, while the female groove portion is supported by the fan case.
Another possible thrust reverser structure comprises an outer assembly in a single piece with no break in the lower portion. Such a structure is called an O structure.
During maintenance operations, in particular in an O thrust reverser structure, it is known to access the inside of the nacelle, and in particular the turbojet engine or an inner structure of the reverser, by separating the outer structure of the downstream section from the nacelle of the concentric inner structure thereof and to translate the outer structure in the downstream direction, in which it simply releases the reverser cascades, so as to allow access to the engine body.
In said O structure, the maintenance between the middle section of the engine and the front frame is done by two female portions generally supported by the front frame and a so-called intermediate case of the middle section, cooperating with an intermediate piece that closes on the female portion, thereby providing the connection between the intermediate case and the front frame of the reverser.
Irrespective of the selected maintenance access mode, C structure or O structure, the cascade vanes still limit access to the heart of the nacelle. It is therefore necessary to retract them if one wishes to provide free access to the heart of the nacelle.
To that end, certain technological embodiments are known based on the disassembly of the cascades to access the cowl surrounding the engine body. Then, the turbojet engine is accessible either due to the presence of hatches, or by disassembling certain portions of the cowl.
Another alternative consists of installing the cascades on a moving front frame. During maintenance operations, the front frame is separated from the intermediate case and the assembly of the sliding cowl, front frame and cascade vanes is translated downstream of the nacelle to provide access to the engine body.
Irrespective of the selected maintenance access mode, such manipulations are lengthy, difficult, and involve installing separating elements in areas that undergo significant structural stresses. Access to the engine is also tedious.